Nonreciprocal circuit element



Nov; 17, 1959 A. G. FO'X NONRECIPROCAL CIRCUIT ELEMENT 3 Sheets-Sheet 1Filed Aug. 6, 1956 INVENTOP A. 6. FOX (Bl 4;,

Arron/V514 NOV. 17, 1959 A. (3, FOX 2,913,678

NONRECIFROCAL CIRCUIT ELEMENT Filed Aug. 6, 1956 5 Sheets-Sheet 2 FIG. 3f

DEVICE d f 1g DEV/CE i FIG. 4 .fl

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Nov. 17, 1959 6. FOX

NONRECIPROCAL cIRcuIT ELEMENT 3 Sheets-Sheet 3 Filed Aug. 6, 1956INVENTOR A. 6. FOX W ME ml muiuq 35% w; 3: an: 3.8

ATTORNEY United States Patent NONRECIPROCAL CIRCUIT ELEIVIENT Arthur G.Fox, Rumson, N.J., assignor to Bell Telephone Laboratories,Incorporated, New York, N.Y., a corporation of New York ApplicationAugust 6, 1956, Serial No. 602,100

6 Claims. (Cl. 333-9) This invention relates to nonreciprocaltransmission circuits for electromagnetic wave energy, and moreparticularly to multibranch networks for establishing nonreciprocalconnections'for electromagnetic wave energy between a plurality ofelectromagnetic wave devices.

It is an object of the invention to couple electromag- 2,913,678Patented Nov. 17, 1959 "ice cession for opposite directions ofpropagation, it will be seen to be nonreciprocal in phase so that ifwave energy is initially applied from a third device to the second pairof conductors, one-half of it will be transferred to the first pair insuch a phase that when the halves are recombined in the hybrid, theyappear in phase in the fourth branch thereof for delivery to a fourthconnected device. The resulting coupling is characteristic. of thecirculator circuit for which numerous uses and applications as acomponent are well known in the art.

Features of the invention reside in the forms of biconjugate or hybridnetwork employed by the invention which are particularly suited for usewith diametrically disposed conductor pairs.

These and other objects, the nature of the present in vention, and itsvarious advantages and features, will appear more fully uponconsideration of the various specific illustrative embodiments shown inthe accompanying netic wave energy from one balanced transmission lineproduced by polarized elements of gyromagnetic material such as ferriteat frequencies of wave energy below a few thousand megacycles. Thesestructures comprise two branch coaxial or balanced transmission linenetworks capable of introducing either a nonreciprocal atten-, nation ora nonreciprocal phase shift to wave energy in the frequency ranges inwhich coaxial and balanced trans! mission lines are used. Thesefrequency ranges include those designated very high frequencyandultrahigh frequency. 1

In accordance with the present invention these tech niques are extendedto a fourebranch coupling circuit known as a circulator. A descriptionof the wave guide or microwave counterpart of this circulator togetherwith its principles of operation and its uses is to be found in anarticle entitled Behavior and Applications of =Ferrites in the MicrowaveRange by A. G. Fox, S- E. Miller and M- T. Weiss, Bell System TechnicalJournal, January 1955, pages 5 through 103. The present inventionfillsthe need for a similar circuit component for use at frequencies belowthe microwave range where wave guide techniques and apparatus arenotapplicable. v

In a particular embodimentof the present invention four conductors arearranged in diametrically-opposite pairs with a longitudinally biasedgyromagnetic element centrally disposed with respect to said conductors.Wave energy components applied from a connected electromaguetic wavedevice to one end of a firstof the pairs will be transferred to thesecond of the pairs by the precessing electrons within the gyromagneticmaterial. As the en- &

ergy propagates toward the other end of the structure, one-half of theapplied energy will eventually .btrans ferred to the second pair in agiven phase. The other ends of the pairs are terminated respectively intwo of the branches of a suitable four-branch biconjugate or hybridnetwork so that the equal components are recomlined in one of theremaining branches of the hybrid for delivery to a, second connecteddevice. Comparing the s r o energy be t e rs bytlg e ectron. a

' chanical and electrical influences but otherwise plays no a balancedelectromagnetic wave device a represented I vectordiiference of saidvoltages in a second output.

in accordance with the invention employing a particular biconjugatenetwork; and

Fig. 6 is a schematic representation of the biconjugate network portionof the embodiment of Fig. 5.

..Referring more particularly to Fig. 1, an illustrative embodiment of acirculator circuit in accordance with the inventionis shown. Thiscircuit comprises four similar, elongated conductors or wires 11 through14 that extend parallel to each other longitudinally and are locatedtransversely at equally spaced points around the circumference of thecircle. The radius of each conductor should be small compared to thedistance between the nearest conductor centers. Thin transverselyextending dielee-I tric spacers 15 and 16 are longitudinally spaced tosupport 'the conductors relative to each other in this relation ship.Support is also provided by a rigid cylindrical shield 17 which may bemade of conductive, nonconductive or electrically dissipative material.Shield 17 protects conductors 11 through 14 from outside mesubstantialpart in the electrical operation of this embodiment.

. The left hand extensions of diametrically opposed conductors 11 and 12comprising one pair are connected to schematically by 18. This devicemay be a source of wave energy, a load circuit or other wave energyutilizmgdevice, or a coupling transducer which in turn couples to asource or a load depending upon the particular application. Theconnection from device 18 to a pair 11'12 is such that couplingisprovided to and from wave: energy of maximum voltage intensity lyingin the plane of the pair. A similar device c, represented schematicallyby 19 is connected to the pair comprising conductors 13 and 14. Theright hand ends of pair 11-12 and a pair 13-14 are connected toahybridnetwork schematically represented by 20 capable of'derivingqvoltages representing the vector sum-of the voltages supportedby the pairs in one output and the terminator four-branch biconjugatenetwork or hybrid" of which many forms, both tuned and untuned, areknown to the art. These networks .all have the property that energyapplied to one branch thereofwill not appear in asecond branch. thereof,but will be'divided into equal: inphase portions in the third and fourthbranches. Energy applied to the second branch 'will not appearinthefirst, but will be divided into equal out -of-phasepor-' tions inthe third and fourth branches. Thus'if equal components that are inphaseaccording to the above characterization are applied by way of pairs 1112and 13 -14 to network 20, the components will combine in the thirdbranch of network 20for delivery'to devicefb' represented by 21.However, if equal component'shaving agrelative phase 180 degreesdifferent from the preceding inphase condition are applied by wayofpairs 1112, 1314, the components will combine inthe fourth branch ofnetwork 20 for delivery to device d represented by 22.

In the region between the left and right ends of the pairs thusarranged, a nonreciprocal coupling is provided by-anelongated cylinderor pencil-shapedelement 26 of gyromagnetic material similarly disposedwith respect to conductors 11 through 14 and extending longitudinallyalong the center of the circle defined by the transverse locations ofthe conductors. Element 26 may be sup ported in this position byextending it through centrally located apertures in spacers 15 and 16. p

The material of element 26 is of the type'havinglelectrical andmagneticproperties of the'type described by the'mathematical analysis of'D.Polder in Philosophical Magazine, January 1949, volume'40,pages"99"throu'gh 115. More specifically, element 26 may be made of anyof the several ferromagnetic materialscombinedin arspinel structure. Forexample, it may comprise-iron oxide with a small quantity of one ormore'bivalent metals such as nickel, magnesium, zinc, manganese;-'aluminum, or other similar material in whichthe other metals combinewith the iron oxide in a spinel structure. This material is known as aferromagnetic spinel or as ferrite. Frequently these materials are firstpowdered and then molded with a small percentage of vplastic materialaccording to the process described in thepublication-of C. L. Hogan, TheMicrowave Gyratorin the Bell- System Technical Journal, January 1952."One specific material which is particularly suitable at thelowerfrequencies contemplated by the present invention ismagnesium-manganese-aluminum ferrite which has been found to exhibit aferromagnetic resonance effect at a lower frequency range thanpriorconsidered .fe'rrites.

.Element 26 is biased by a polarizing magn'eticfield appliedparallel toconductors 11 through-14. This-field may be supplied by a solenoid 27mounted upon the out-' sideof shield 17 and supplied by an energizingcurrent from source 28 through rheostat 29. It should be noted,-however, that element 26 may be magnetized bye-solenoid of othersuitable physical design, by a permanent magnet structure, or thematerial of element26 maybe permanently magnetized.v

The coupling produced by element 26 can'be ex-- plained by therecognition that'the'gyromagnetic material off element. 26 containsunpaired electron spins which' tendio line up with the applied field.These spins have an. associated magnetic moment which can be made toprecess about the line of the biasing magnetic field,ikeeping. anessentially constant moment component'in the direction of the appliedbiasing field'and'at the same timeaproviding a moment component whichmayrota'w iita plane normal to the field direction. Thus'rwhen 'areciprocating high frequency magnetic-field ofelectro magnetic waveenergy is impressed upon theinonieifi; the; moment will commence toprecess in.one;angn1ar"sense;

The-combined effectof many such electrons and 'ltlieirterial not only aflux representing the impressed magnctic'field' but" also a fluxrepresenting areciprocating" field at right angles in space to theapplied field and displaced in time from the applied field by a phasedetermined by the direction of precession of the electrons andindependent of the direction of propagation of a wave along the lines.The amplitude of the coupled wave depends uponthe parameters of theferrite and may also be controlled by the strength of the biasingmagnetic field.

Thus, when an electromagnetic wave is applied from device a to pair1112, an electric field will be setup between the'conductors with amagnetic field concentric with each conductor and having a maximumconcentration extending between the conductors in a plane normal to theplane of the conductors. When this field encounters element 26 aninduced magnetic field will be produced normal to the exciting fieldwhich in turn produces an electric field extending between pair 1314.Initially, this induced field will be small but as the distance from theexcited end is increased, the field becomes increasingly larger. At anappropriate electrical distance. to the right, depending in a givenstructure upon its physical length and the'biasing field strength, theinduced field contains one-half of the energy. For the biasing fieldpolarity indicated on the drawing, the phase of thisinduced energyrelative to the remaining portion of the excited energy on pair 1112 issuch that when com ductor 11 is positive with respect to conductor 12,conductor 13 is positive with respect to conductor 14. Defining thisrelation as inphase, the two components will appear in one of theoutputs of network 20, defined as the inphase output, for delivery todevice I). If a voltage wave had been initially applied to pair 13-14,however, as from device c, the constant direction of electron precessionwithin element 26 will induce on pain 11'---12'an out-of-phase voltagemaking conductor 12 positive with respect to conductor 11 when conductor13- is positive with respect to conductor 14. These two components willthen appear in the other output of network 20, defined as theout-of-phase output, for delivery to'device'd;

The coupling'thus far established is schematically represented on Fig. 2by the radial arrows a, b, c and d associated with the ring 24 and arrow25 diametrically indicating the coupling. from a to b and c to d.

If energy'were applied from device b acting now as a source of waveenergy, it will be divided by network 20- into equal inphase componentsupon pairs 11 12 and 13-14 for propagation to the left. Sincethetransfer ofenergy between the pairs is antireciprocal, i.e. itcontinues in thesanie sense regardless of the direction of propagation,the components supported between pair 1112willl betransferred to pair1314 as the wave propagatesto the" left for delivery to device c. Thistransmission is indicated schematically on Fig. 2 by the arrow 25whichindicates coupling between b and 0. Similarly, if energy:isintroduced initially from device d, it will appear at the left handend 1112 for delivery to device a. Thiscoupling is similarly indicatedon Fig. 2 by the schematiccoupling between branches d and a. Thus eachbranch is coupled around thecircle 24 toonly one other terminal foragiven direction of transmission but to adifferentterminal for theopposite direction of transmission. This i'sthe characteristic typicalof the group of coupling circuits'known as circulators.

Referring to Fig. 3, a biconjugated network of resistance's isillustrated that may be' employed for network 20 of Fig. 1. Asillustrated, this network comprises four, equal center tappedresistances 31 through 34 arranged in abridge; The center tapofresistance 34 would be connected to conductor 11, as illustrated, andthe center tap of 'resistance 31, 32 and 33 would similarly bacon nectedto conductors 14, 12 and 13 respectively; The

associated moments produces in? the 'gyromagnetic meeireuirsnpplyingdevice'b is connected between the com when equalvoltages are applied across pair 11-12 with conductor 11 positive andacross pair 13-14 with conductor 14 positive as represented by thesymbols associated on the drawing with the conductors, the individualcontributions are additive for device b and cancel at de- 'vice d. (Ifeither one of the-voltages represented is reversed in'phase, the sumwill appear at device d and cancel at device [2. The advantages of sucha network are its simplicity and broad band while its disadvantage liesin the power lost through dissipation in the resistance.

A biconjugate network having negligible dissipation and suitable for useat relatively low frequencies is shown in Fig. 4 and comprises a centertapped inductance or autotransformer 41 connected between conductors 11and 12 with the center tap 42 connected to conductor 13, a transformer43 having its primary connected between conductors 11 and 114, and atransformer 44 having its primary connected between conductors 14 and12. If equal voltages are applied across pair 11-12 with conductor 11positve and pair 13-14 with conductor 14 positive as represented by thesymbols associated with the conductors, the contributions are additivein the secondary of transformer 44 for delivery to device b and are incancelling relationship in the secondary of transformer 43. On the otherhand, if either voltage applied 7 to the conductor pairs is reversed inphase, wave energy is delivered to device d and not to device b. Itshould be understood that Figs. 3 and 4 are illustrative of only twosuitable biconjugate circuits which are adaptable to the principles ofthe invention. The adaptation of other circuits will readily occur toone skilled in the art.

Fig. illustrates a novel form. of biconjugate network that isparticularly well suited for use in the present invention at higherfrequencies. This circuit is specifically disclosed and claimed in mycopending application Serial No. 602,101, filed August 6, 1956.Essentially this net work comprises four quarter wave shorted sectionsof transmission line connected between adjacent ones of conductors 11through 14 with the shorted point of each line being made available asone output terminal. As shown on Fig. 5, supporting shield 17 of astructure substantially identical to that disclosed in Fig. 1, extendsto the right an odd multiple of one-quarter wave lengths of the meansoperating frequency. The right hand end of shield 17 is closed bydielectric spacer 50 similar to spacers 15 and 16. Shield 17 and spacer50 provide support for the right hand ends of eight conductive elements51 through 58 which each extend, in the manner to be described, from theright hand end of one of conductors 11 through 14 through one of thefour apertures 59 provided in spacer 50 to receive the conductors. Eachof apertures 59 is displaced about the longitudinal axis of thestructure 45 degrees from or midway between the two circumferentiallyadjacent apertures in spacer 16. Four conductive elements 61 through 64emerge to the right of spacer 50 and form the two orthoganally relatedconductor pairs or output branches which are in turn connected todevices b and d. More particularly, each conductor of the first group 11through 14 is joined with or forks with two conductors of the group 51through 58 each of which in turn is connected to one of thecircumferentially adjacent output conductors. For example, conductor 13of pair 13-14 is connected by conductor 53 to conductor 62 of pair 62-64and by conductor 54 to conductor 63 of pair 63-61. Similarly, conductor14 of pair 13-14 is connected by conductor 57 to conductor 64 of pair62-64 and by conductor 58 to conductor 61 of pair 63-61.

In like manner the conductors 11 and 12 of pair 11-12 are connected byconductors 51 and 52, and by conductors 55 and 56 to the conductors ofthe output pairs.

The diameters of conductors 51 through 58 are preferably smaller thanthe diameters of conductors 11 through 14 and 61 through 64 with thediameters relatively p'roportioned according to principles familiar tothe art so that an impedance match is obtained between a singleconductor, such as 13, at the point where it forms a junction with adouble conductor such as 53 and 54.

Electrically, conductors 51 through 58 appear as sche-.

matically represented in Fig. 6 and constitute means for coupling to andfrom a resultant of the total energy sup.-v

ported by pair 11-12 and pair 13-14 that lies at 45 degrees to the planeof either of the pairs. Thus, if equal voltages are appliedacross pair11-12 with conductor 11 positive and across pair 13-14 withconductor 14positive, as represented on Fig. 6 by the symbols on the conductors, avoltage appears across pair 61-63 with conductor 61 positive andconductor 63 negative, representing the resultant of the two originalvoltages. .No voltage appears between conductors 62 and 64 which are atthe same potential. The nature of the quarter twave line 56-57 is suchthat it presents a high impedance between conductors 12 and 14 and line53-52 between conductors 13 and 11. If either one or" the voltages onpair 11-12 or pair 13-14 is reversed, the resultant will appear betweenconductors 62 and 64 with no voltage be tween 63 and 61. 7

In all cases it isu'nderstood that the above-described arrangements areillustrative of a small number of the many specific embodiments whichcan represent applications of the principles of the invention. Numerousand varied other arrangements can readily be devised in accordance withthese principles by those skilled in the art without departing from thespirit and scope of the invention.

What is claimed is:

1. A nonreciprocal component comprising a plurality of elongatedconductors being disposed symmetrically relative to each other indiametrically opposite pairs with each conductor of one pair havingadjacent to it conductors of the other pair, an elongated element ofpolarized gyromagnetic material centrally disposed with respect to saidconductors, saidconductors and said element being parallel to each otherbetween their longitudinal ends, means for coupling electromagnetic waveenergy supported between the conductors of one of said pairs to and fromone end of said pair, means for coupling electromagnetic wave energysupported between the conductors of the other of said pairs to and fromone end of said other pair, and a four-branch biconjugate network havingtwo of its branches connected respectively to the other ends of each ofsaid pairs with the remaining two of said branches comprising means forcoupling electromagnetic wave energy to and from said network.

2. The combination according to claim 1 wherein said biconjugate networkcomprises'a bridge of four center tapped resistances in whichconnections between opposite center taps comprises two of said branchesand in which connection between opposite junctions comprises theremaining two of said branches.

3. The combination according to claim 1 wherein said biconjugate networkcomprises quarter wave shorted stubs connected between adjacentconductors, said remaining branches comprising the connections betweenthe shorted point of oppositely disposed stubs.

4. A nonreciprocal coupling element comprising first and second pairs oftransmission lines each comprising two elongated conductors spaced fromand extending longitudinally parallel to and conductivelyisolated fromeach other along a major portion of their lengths, means for couplingsaid lines with a nonreciprocal coupling comprising a polarized elementof gyromagnetic material extending in a space occupied in common by themagnetic fields of voltage waves conducted between said lines, and afour-branch biconjugate network having two branches thereof connectedone each across said first and second pairs at one of their ends.

5. The combination according to claim 4 including an electromagneticwave device connected across the other endsrofleachioflsaid pairs andan' electromagnetic WaV6- device' connectedacross each of the remainingbranches of said bic'onjugate'network.

- 6::A vnonreciprocal component comprising a plurality elongatedconductors being disposed symmetrically around the circumference of acircle With one conductor diametricallyropposite each conductor and twoconductors circumferentially adjacent each conductor, an elongatedelement of polarized gyromagnetic material centrally disposed-withrespect to said conductors, said conductors and 10 2,788,396

said-element being parallel to each other between their longitudinalends, means for coupling electromagnetic wave energyvsupported betweenone pair of opposite conductors to and from one end of said pair, meansfor coupling electromagnetic. wave energy supported between another pairof opposite conductors to and from one end of said'pa-ir, and means forbridging the other ends of adjacent conductorsto derive a voltagerepresenting the vec-- tor sum of the voltages supported by the twopairs for: delivery to one circuit and to derive a voltage representing,

the vector'ditference of said voltages for delivery to a second circuit.

References Cited in the file of this patent UNITED STATES PATENTS

